The present invention is directed generally to ion plating, and more particularly to an improved gasless ion plating process and apparatus.
Ion plating is becoming well known in the art. It has been found to be particularly advantageous because the plating process is three-dimensional, allowing a substrate of virtually any shape or configuration to be uniformly plated with plating material. By utilizing gasless ion plating, most any type of material, both conductive and non-conductive, may be plated without requiring drastic alterations of plating parameters. Furthermore, the adherence between the plated material and the substrate has been found to be far superior to that obtainable with other plating processes.
Prior art gasless ion plating processes, such as that disclosed in White, U.S. Pat. No. 4,039,416, contemplate the carrying out of the ion plating process in an evacuated chamber wherein the substrate to be plated is placed. The substrate is first placed into the chamber and then the chamber is evacuated. Within the chamber there is disposed a plating source including plating material and means for heating and vaporizing the plating material. One such plating source is fully described in White, U.S. Pat. No. 4,016,389, and is referred to as a high rate ion plating source. This source includes a crucible in which the plating material is placed and a coil wound about the crucible. The center of the coil is connected to ground potential and the coil ends are connected to an alternating current power source. The power source and coil heat the crucible to melt, vaporize and partially ionize the plating material.
As the plating material is vaporized, a radio frequency power supply coupled to the substrate to be plated creates a plasma of positively charged plating ions from the vaporized plating material about the substrate. A negative direct current bias is developed on the substrate by either applying a direct current negative voltage directly to the substrate in the case of a conductive substrate or in the case of a non-conductive substrate, by relying upon the self-biasing effect of the substrate by virtue of the radio frequency field within the chamber. The negative bias on the substrate causes the positive plating ions to be accelerated toward the substrate for plating the substrate.
While gasless ion plating processes of the type described above have been found to be extremely useful and to exhibit advantages over other plating processes, there remains substantial room for improvement therein for carrying out such a process on a mass production type basis. For example, prior gasless ion plating processes have required the substrate and substrate support means to be electrically insulated or isolated from any portion of the chamber by virtue of the fact that the chamber is preferably connected to ground potential to eliminate the electrical shock hazard to which operating personnel would otherwise be exposed. As can be appreciated, such electrical isolation is required due to the fact that radio frequency energy and a negative direct current voltage is applied directly to the substrate support means.
In mass production environments, it is desirable to vary the orientation of the substrates during the plating process to assure plating of the entire substrate to a uniform thickness. This is commonly accomplished by rotating the individual carriers upon which the substrates rest. Because the substrates must be electrically isolated from the chamber or any portion thereof, specialized insulating bearing elements are required to provide the required movement of the substrates while maintaining the required electrical isolation between the substrate and any portion of the chamber. Furthermore, in order to impress the required negative direct current voltage on the substrates, a commutator ring has been utilized. The commutator ring is connected to the required radio frequency signal and negative voltage and to the individual substrates by a slip-type connection. This system can cause intermittent biasing and consumes valuable space within the chamber. Additionally, the resulting required power fed through into the vacuum system as well as the extreme number of moving parts required create the possibility of malfunction and failures.
It is therefore a general object of the present invention to provide a new and improved gasless ion plating process and apparatus.
It is another object of the present invention to provide such a process and apparatus wherein electrical isolation is not required between the substrates to be plated and any portion of the chamber.
It is a still further object of the present invention to provide an improved gasless ion plating process and method wherein the electric field within the chamber for accelerating the positively charged plating ions toward the substrates is produced by developing a positive direct current bias on the plating source.
It is a still further object of the present invention to provide such a gasless ion plating process and method wherein radio frequency energy is applied to the plating source as opposed to being applied to the substrates to thereby eliminate the heretofore required commutator rings or the like.